1. Field of the Invention
The present invention relates to a power transmission system having a torque transmission elastic member, specifically relates to a power transmission system suitable for being built into a compressor of a vehicular air-conditioning system.
2. Description of the Related Art
For example, in a vehicular air-conditioning system, as a power transmission system transmitting power from an engine, motor, or other external power source to a compressor forming part of a refrigeration cycle, a power transmission system not having an electromagnetic clutch mechanism, but having a torque limiter is being used. This power transmission system transmits power between a pulley driven by an external power source and a hub fixed to a shaft of the compressor. The hub is provided with a rubber or other damper attenuation mechanism and is arranged coaxially with a pulley. In the past, the pulley and hub were fastened together using insert hardware and bolts, but in recent years, a power transmission system has been proposed which makes the pulley out of plastic, forms a projection at the outside ring of the hub, forms a recess at the inner circumference of the plastic pulley, and fits these together and therefore does not require any bolts for engagement of the hub and pulley (see Japanese Patent Publication (A) No. 2002-3646671).
However, in the prior art, there was the problem that excess torque or torque fluctuations caused the projection of the outside ring of the hub and recess of the pulley to directly contact and caused the recess of the plastic pulley, which is inferior to the projection of the outside ring in strength and abrasion resistance, to end up being abnormally abraded.
The assignee proposed a power transmission system for dealing with this problem provided with a hub comprised of a pulley, inner hub, outer hub, and torque transmission elastic member and engaging hub engagement parts comprised of an elastic material provided at the inner circumference, outer circumference, or inner and outer circumferences of the outer hub and a pulley side engagement part provided at a position of the pulley corresponding to the outer hub so as to form a torque transmission structure of a hub and pulley (Japanese Patent Application No. 2005-69316). Due to this, no bolts or insert hardware is required and higher strength attachment of the pulley and hub can be obtained.
In the proposed power transmission system, the torque transmission elastic member and hub side engagement part are preferably integrally molded with the hub. In this case, for example when integrally molding a plastic elastic member and a metal hub, normally a plurality of injection gates are arranged near the center of the location for forming the elastic member forming the cylindrical part between the inner hub and outer hub and these gates are used to inject the material of the elastic member. However, the bases of the gate marks remaining after integral molding have small radii of curvature. If a load susceptible to torque fluctuations is received frequently over a long time, stress concentrates near the gate marks possibly leading to deformation or even breakage.